The present invention relates to a process for producing and use of maleic acid (co-)polymer salt improved in biodegradability. In detail, it relates to a process for producing a maleic acid (co-)polymer salt improved in biodegradability, which is very useful as a detergent building, a scale inhibitor, and various kinds of chelating agents etc., by using a specially defined polymerization catalyzer and a specially defined polymerization method, with high efficiency and cheap cost, and also, relates to the use as a detergent building and a scale inhibitor etc.
As a detergent building, a scale inhibitor, and a chelating agent etc., an additive based on phosphorus, such as a condensed phosphoric acid salt and a phosphoric acid salt, has so far been used. However, when run into the sea or lake through a river etc., these become an original substance for a red tide etc., so that their use is very limited. Thus, instead of a phosphorus additive, an additive in a series of polycarboxylic acid salts has practically been used in recent years in the forementioned field and in large quantity. However, the polycarboxylic acid salts additive which have so far been used are all poor in the biodegradability and, for example, in a case where it is used in large quantity as a detergent building or a scale inhibitor etc., there may take place such a greatly serious problem as the accumulation in circumstances.
For example, although there is proposed a maleic acid (co-)polymer (salt), which is obtained with polymerization in a mixed solvent of water and a primary alcohol or carbon number 1 4 or a ketone of carbon number 3 4 in Japanese Official Patent Provisional Publication, showa 62-91295, and Japanese Official Patent Provisional Publication, showa 62-91296, the maleic acid (co-)polymer (salt) thus published was low in the biodegradability and insufficient in properties useful as a scale inhibitor. Besides, in these arts, a maleic acid (co-)polymer (salt) of high polymerization percentage was not obtained. Also, although there are proposed maleic acid (co-)polymer salts obtained by a polymerization in water solvent in the presence of hydrogen peroxide, which were described in Japanese Official Patent Provisional Publications, showa 57-168906 (U.S. Pat. No. 4,519,920), showa 59-64615 (U.S. Pat. No. 4,668,735), showa 59-176312 (U.S. Pat. No. 4,589,995), showa 59-210913, showa 59-21374, showa 60-212410, showa 60-212411 (U.S. Pat. No. 4,709,091), showa 60-212412, showa 612-178097, showa 62-218407 (U.S. Pat. No. 4,659,793), showa 63-114986, showa 63-235313, and showa 63-236600, the maleic acid (co-)polymer salts thus published show very inferior biodegradability. There is no description about the biodegradability in all said literatures.
On the other hand, although there is described in "YUKAGAKU, 35, 937 (1986)" that sodium poly-.beta.-DL-malic acid, which is formed with ring-opening polymerization of malolactons, shows high biodegradation percentage, properties of this polymer as a detergent building are unsufficient, and the synthesis of this polymer requires a complex process, so that the industrial utility is low. Also, there is described that a polymer of .alpha.-hydroxyacrylic acid shows biodegradability, but this polymer decomposes only with specially defined bacteria, and the synthesis and this polymer requires a complex process and, as a result, it becomes very expensive, so that the industrial utility is low.
Therefore, there has been greatly desired a process with which a polycarboxylioc acid salt which has useful biodegradability as a detergent builder, a scale inhibitor, and various kinds of chelating agents etc. is produced with cheap cost and in a high yield.